Degradation Characteristics of Ballast in the Field and their Measurement

In service, the ballast layer is subject to both deformation and degradation due to traffic load. Therefore, in order to keep the track performance within the required standards, the ballasted foundation is subjected to various maintenance cycles such as tamping, ballast cleaning or reconstruction processes. A better planning of these processes can lead to an extension of ballast life and a reduction in the maintenance costs. In practice, the extent of ballast fouling is usually based on visual inspections by track staff. Also, the current ballast fouling index does not realistically estimate the extent of ballast fouling. Therefore, ballast cleaning is not programmed as effectively as might be possible if a correct evaluation of the degree of ballast fouling were to be carried out. This paper presents the degradation characteristic of the ballast layer and its effect on the ballast foundation performance is discussed. The shortcomings of the currently used ballast fouling index are then identified. Based on the analysis of an extensive number of field samples, a new fouling index has been proposed, which properly quantifies the extent of ballast fouling. The corresponding classification criteria are also presented. Furthermore, the paper presents a method of estimating the ballast life, thus leading to a reduction in the maintenance costs due to more efficient maintenance programming.